White blood cells are your warrior cells. They are the part of the immune system that attack and get rid of viruses and bad bacteria that could harm your body.

T cells are a type of white blood cell. Their main functions are:
1. To kill off other cells that have been infected by viruses or cancer
2. To help B cells, which is another type of white blood cell, to recognize viruses and produce antibodies

T cells have been extensively studied in 2020 and several studies have concluded that T cells aid in fighting off Covid-19.
Simply put, the stronger your T cells are, the better your immunity will be in fighting off Covid-19, as well as cancer and other types of viruses.
Check out this article on T-cells vs. Covid-19.

Hydrogen plays an important role in strengthening your T cells, as many independent research studies have suggested.

Patients with cancer who were on hydrogen saw either a strengthening of their T cells, and/or a reduction in the progression of cancer cells.

Sneak a peak at the various number of health issues that hydrogen has had good results with.

For more information on white blood cells, Loving Biology has a great, concise overview on the roles of white blood cells.